September 21, 1900.] 



SCIENCE. 



439 



decern- lineata, the latter form extending 

 northward along the eastern slope of the 

 western highlands, and west of the arid 

 region, spread as far north as the Canadian 

 boundary, and perhaps even farther. 



The low humid Gulf coast area also pro- 

 duced a characteristic form, L.juneta, which 

 can be traced into the parent form in the 

 lower part of the Mexican region, and which 

 spread up the Mississippi valley into south- 

 ern Illinois, and along the Gulf, and up the 

 Atlantic coast to Maryland. 



Such was the distribution of these beetles 

 until the middle of the nineteenth century. 

 About 1840 the potato began to be culti- 

 vated in the cafions of Colorado, and L. 

 decem-lineata soon left its old food plant, 

 Solanum rostratum, for the new S. tuberosum, 

 causing, no doubt a rapid increase in the 

 number of the species. In 1849-50 began 

 the rush to California from Council Bluffs 

 west along the Platte river. There are 

 several accounts extant of the sale of pota- 

 toes to emigrants by thrifty Irishmen at 

 Omaha and Council Bluffs, and judging from 

 the haste and carelessness of the emigrants 

 there can be no doubt that potatoes were 

 lost or thrown away along the route. The 

 valley being fairly fertile and moist, these 

 potatoes grew until there was a more or 

 less continuous line of potato plants from 

 Council Bluffs along the Platte river to the 

 canons of the Colorado region. Along this 

 route L. decem-lineata moved eastward so 

 that in 1859, ten years after the '49 rush to 

 California, the beetle is reported as injuri- 

 ous to crops at a point just east of the arid 

 belt and about on the 98th meridian. Dur- 

 ing the next twenty years it reached the 

 Atlantic coast and covered the entire coun- 

 try between latitudes 37° and 47° north. 



Connected with the advance of this form 

 there are several features of general inter- 

 est. The beetle is double-brooded over the 

 whole area, but it is only the second, or 

 August brood, that flies to any great ex- 



tent, and, consequently, has pushed into 

 the hitherto unoccupied territory. How- 

 ever, the new areas covered have not been 

 overrun by the unaided flying of the beetles 

 eastward. If no outside agent were at work 

 the beetles would fly west as often as east, 

 so that alone no great advance would be 

 made. It is to be noted that the beetle is 

 not a strong flyer, that it is unable to ad- 

 vance successfully against the wind, and 

 that the direction of its flight is, therefore, 

 controlled largely by the wind. In August 

 and September there are established certain 

 well defined wind tracts, and it is along 

 these that the beetle has advanced with 

 the greatest rapidity, the advance being di- 

 rectly proportional to the wind velocity in 

 any region for a given year. The most 

 rapid advance has been in the track of the 

 prevailing westerlies along the lakes and 

 down the St. Lawrence valley. This point 

 is proved by contrasting the northern ad- 

 vance with the extremely slow advance 

 southward, the latter being due in part to the 

 temperature and moisture conditions, but 

 largely to the variable winds of the south- 

 ern part of the United States in late summer. 



The entire advance of this form east of 

 the arid belt has been independent of lines 

 of travel, there being no evidence of any 

 considerable transportation by human agen- 

 cies. 



At the present time the beetle is found 

 throughout all that portion of Xorth Amer- 

 ica which lies east of the Eocky Mountains 

 and between latitudes 32° and 55° north. It 

 has been found as far north as 65°, but to 

 my knowledge has not gained a foothold in 

 Labrador or Newfoundland. 



It is interesting to note that as L. decem- 

 lineata has advanced L. juncta has retreated 

 before it. Formerly juncta was abundant 

 in southern Illinois, and in Delaware, Mary- 

 land and New Jersey, but now it has re- 

 treated to the Carolinas on the Atlantic coast 

 and to lower Mississippi on the south. 



